1. Field of the Invention
This invention relates generally to cassettes of the type including a length of magnetic tape wound around at least one reel rotatably mounted in a housing with a portion of the tape extending to the exterior of the cassette for engagement by a recording and/or reproducing device and, in particular, a slack limiter for frictionally engaging the tape and limiting looseness or slack in the portion of the tape extending exteriorly of the cassette.
2. Description of the Prior Art
While the subject matter of the invention has general utility with respect to one-quarter inch audio magnetic tape cassettes, one-half inch videotape of either the VHS or Beta formats, and three-quarter inch videotape cassettes, for simplicity the invention will be described with respect to one-half and three-quarter inch magnetic videotape cassettes which include two reels mounted within a housing with a length of magnetic tape wound around the two reels and extending between the reels.
Slack or looseness in the length of tape between the reels in such a cassette can arise when the cassette is being transported or is otherwise separated from its associated recording and/or reproducing device, which device is commonly referred to as a videotape recorder (VTR). While some cassettes have locks which restrict rotation of the reels when the cassette is not in the VTR, it is still possible that one or both of the reels within the cassette housing may turn to unwind the tape and develop slack in the portion of the tape extending between the reels. Slack in the tape can also occur when the tape is engaged with the VTR. Typically, the VTR has spindles which engage the two reels. If driving and braking of the reels during the operation of the VTR is not synchronous, slack in the tape will develop. This slack may cause the tape to jam within the cassette housing or within the VTR and may lead to defective recording or reproducing operations.
So-called slack limiters for avoiding such slack or looseness of the magnetic tape have been disclosed in U.S. Pat. Nos. 3,797,779; 4,290,567; and 4,342,436 in which the slack limiters described commonly include a resilient, flexible strip, usually of plastic, affixed at one end to the cassette housing and having a free end coated with a layer of low friction material such as poolytetrafluoroethylene (Teflon). The free end of the slack limiter presses the magnetic tape against a stationary portion of the cassette housing and thus frictionally prevents the magnetic tape from unwinding from the reel and developing slack. In addition, as described in U.S. Pat. No. 4,342,436, the slack limiter may be double-ended, in which case a second free end of the slack limiter biases the magnetic tape outwardly from the cassette housing while the first free end performs the function described above.
The foregoing patents are distinguished by the manner in which the slack limiter is attached to the cassette housing. In U.S. Pat. No. 3,797,779, the slack limiter is affixed to the cassette housing with an adhesive. This method of attachment is relatively inefficient since the adhesive may deteriorate with age and eventually give way, allowing the slack limiter to fall from or within the cassette housing. Further, manufacturing costs are high because a number of steps are required for assembly and it is very difficult to automatically mount a slack limiter which is retained adhesively.
Alternatively, U.S. Pat. Nos. 4,290,567 and 4,342,436 disclose methods for mechanically attaching the slack limiter to the cassette housing in which a notch or slot formed in the slack limiter is engaged by a projection located within a receptacle formed in the housing. These methods have proven effective in retaining the slack limiter within the cassette housing, but a tolerance must be provided between the notch or slot and the housing projection, so movement of the slack limiter with respect to the cassette housing and the magnetic tape is likely. This movement of the slack limiter may result in less than full contact between the slack limiter and the magnetic tape, detrimental contact between a sharp edge of the slack limiter and the tape, or mistracking of the tape through the cassette.
With respect to the slack limiter itself, it is a continuing goal to reduce manufacturing costs by reducing the number of operations which must be performed to produce the slack limiter and reducing the precision with which the slack limiter must be constructed without sacrificing precise positioning of the slack limiter within the cassette housing.